Rollup merge of #37484 - pfrenssen:patch-1, r=steveklabnik
Rollup merge of #37484 - pfrenssen:patch-1, r=steveklabnik

Update "Testing" chapter for 1.12

I followed the "Testing" chapter using Rust 1.12.1 but there are some differences. By default the `tests` module is now also generated by `cargo new`, and the console output is updated.

graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust